It depends on how much you can lift in general. There is no set weight per height/weight ratio.
Really make sure that you get the form down with very light (even just the bar) weight. This will help immensely in preventing injuries.
Lunges will be a lighter weight than squats because of the mechanics. As a basic starting place (and when you have your form down) I would try doing squats 3 sets of 8-10 reps with half of your body weight. If you can do that, then next time add weight (10-15%), if you can't do that, lower the weight and go from there. It might take a few workouts for you to figure out where the weights should be.
Hope that helps some.
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